Many marijuana growers know that enriching the air in their grow rooms and greenhouses can really affect yield. Operating CO2 generating equipment properly can be a bit tricky, and dangerous if done incorrectly. To address this issue several companies offer fantastic equipment designed to control CO2 generating appliances. These controllers are really the best way to sequence your enrichment cycles but are rather expensive. There is of course another way, we can approximate appropriate enrichment periods using this simple formula.
Room Volume (adjusted target CO2 Concentration) ---------------------------------------------- = Burn time*, in minutes to reach target CO2 input/min
*If you are using bottled CO2 just replace the term ‘burn’ with ‘on’, the math works exactly the same any enrichment method what has a measurable output. Use this link if you don’t like math.
Before we begin with the equations lets establish a hypothetical situation. Let us say you just purchased a propane burning CO2 generator which produces 13 cubic feet of CO2/hour, in fact lets say it’s a C.A.P. GEN-1. Next lets pretend your grow room or greenhouse is 10’x10’x’10’, I chose these even numbers to simplify the math. Finally we should establish an approximate ambient CO2 concentration for your area. Atmospheric CO2 tends to range from 300-600ppm, expect to find higher levels of CO2 in busy cities and lower levels in rural areas. For this example lets assume your grow room is in the country with an ambient CO2 concentration of 300ppm.
Lets recap the parameters we’ve established;
- Output of CO2 generating appliance = 13 cubic feet/hour
- Grow room or greenhouse dimensions = 10’x10’x10’
- Ambient CO2 concentration = 300ppm
Calculating Room Volume
So we have some numbers to work with but they are not quite ready to enter into my equation. Before we begin, we need to convert your room dimensions into a volumetric value expressed in cubic foot units. I will demonstrate;
Length x Width x Height = Volume 10’x10’x10’= 100’x10’= 1000 cubic feet
Calculating target CO2 Concentration and Adjusting for Ambient
Marijuana plants are theoretically capable of processing CO2 in concentrations as high as 2000ppm, however, this is dependent on many factors and requires that every other facet of plant health is in perfect balance. Laboratory trials on plants often fail to meet these requirements or are only able to maintain the balance for a short time, for this reason 1800ppm is often considered to be ideal CO2 level. Concentrations beyond 1800ppm offer only diminishing return. For this tutorial let us use 1800ppm as our CO2 concentration target.
We have already established your ambient atmospheric level as 300ppm so we can now subtract that from the target CO2 value.
Target CO2 concentration - ambient atmospheric = adjusted value example: 1800ppm - 300ppm = 1500ppm
Next, to greatly simplify the math we will convert our CO2 value from parts per million into a decimal value. To do this simply multiply your ppm value by 0.000001, or use this idiot proof calculator. Lets input our values;
ppm value x 0.000001 = decimal value example: 1500 x 0.000001 = .0015
Converting CO2 generator output
Now we need to convert our burner output into cubic feet per minute. The generator used in this tutorial has an output of 13 cubic feet per hour, to convert simply divide this value by 60.
output in cubic feet per hour/ 60 = output in cubic feet per minute example: 13 / 60 = .216 cubic feet per minute
Build your Equation
Room Volume (adjusted target CO2 Concentration) --------------------------------------------- CO2 input/min
Next, lets insert our example variables and solve;
1000(.0015) ------------- .216=
1.5 ---- = 6.9 .216
What it all means
So according to the math our pretend grow room should reach 1800ppm CO2 concentration after a 7 minute burn from our C.A.P. Gen-1. This may be the case if our room was sealed and if several other variables like elevation, temperature and barometric pressure are kept “nominal”. But, its close enough, and as good as we’re going to get without using specialized equipment.
There are other factors to consider too, a 7 minute burn will likely raise room temperatures which could trigger an automated exhaust cycle. Also your plants will be busy converting the CO2 into oxygen which will lower the overall saturation. Finding this balance between temperature and atmospheric enrichment is part of fine tuning the room, and every room is different.
CO2 Generating Appliance output
Most of the time you can find the output rating of your CO2 generating appliance printed on it’s packaging, housing or attached literature. If your propane or natural gas burning appliance was not built with CO2 enrichment as it’s primary function you can still determine its CO2 output by using it’s BTU output. This is rarely the case and probably only applies to growers who want to use their propane burning water heater or furnace to enrich their garden or greenhouse.
Marijuana Growers HQ does not recommend use of household, gas burning appliances for CO2 enrichment but it can be done. Diverting vent gas from your water heater or furnace into your home is VERY dangerous and has lethal potential.
To convert BTU output to CO2 output use the following formulas;
Btu/Hour(1.18) ------------- 1000
Btu/Hour --------- 1000
Of course, different ways of introducing these exhaust gasses would be needed. Water heaters turn on and off on their own schedule. Perhaps another reason not to try something foolish like this, but above are the conversions anyway.
Calculating CO2 Enrichment,